The invention relates to a device for presenting lids to moving sealing stations in a heat-sealing machine.
In general, a heat-sealing carousel comprises a turntable with a plurality of stations disposed around its periphery for heat-sealing receptacles, each station heat-sealing a lid onto a receptacle between the receptacle being introduced to the turntable and being ejected from the turntable. A difficulty with heat-sealing devices lies in producing and positioning lids so as to be immediately adjacent to the openings of receptacles without interfering with the receptacles or the heat-sealing heads.
Document FR-A-2 688 192 discloses a heat-sealing carousel comprising a series of moving heat-sealing stations, each station being fitted with a lid presenting device comprising a lid production module having a member fitted with a tool for cutting lids from a strip, and a gripping clamp placed facing the lid production module to pull the strip before actuating the cutting tool.
Since there are as many presentation devices as there are sealing stations on the carousel, the structure of such carousels is bulky, complex, and expensive to manufacture. In addition, replacing reels of heat-sealing strip requires the carousel to be stopped, to the detriment of production throughput.
The invention provides a device for presenting lids to moving sealing stations, the device comprising at least one lid production module mounted stationary facing a path of the sealing stations and having a lid cutting member fitted with a tool for cutting lids from a strip, and also having gripping members secured to the sealing stations, the gripping members being placed relative to the lid production module so as to take hold of a lid on the fly.
Thus, a single lid production module can be used for all of the sealing stations, such that the general structure of the sealing machine is considerably simplified, while nevertheless ensuring that lids are held accurately in position by means of gripping members associated with each station.
In an advantageous version of the invention, the lid production module includes a member for advancing lids disposed downstream from the cutting tool.
It is thus possible to increase the distance between the cutting tool and the moving stations sufficiently to have all the space required for giving good accessibility to the lid production module without any risk of interference with the sealing heads.
Advantageously, the lid cutting member includes a support for two reels of strip, and a selector suitable for causing one of the strips to advance towards the cutting tool for cutting up the strip downstream from the selector.
It is thus possible to change one of the reels without stopping the production of lids.
Also advantageously, the selector comprises three rollers having parallel axes and mounted to enable one of them to move relative to the other two between two extreme positions, in each of which positions two rollers co-operate to pinch one of the strips, at least one of the two rollers between which a strip is pinched being a drive roller.
The advancing strip is thus selected merely by switching the movable roller from one extreme position to the other.
Preferably, the selector has two brakes arranged to act positively on the strip which is not being pinched in order to stop it from moving.
This provides positive braking of the non-advanced strip(s), thereby eliminating the risk of two strips interfering with each other.
Furthermore, in existing devices, the cutting tool is generally of the guillotine or scissor type, which means that the strip must be stopped in order to be cut.
In an aspect of the invention, the cutting tool comprises both a rotary blade-carrier fitted with at least one blade having a cutting edge and a rotary backing cylinder, the blade-carrier and the backing cylinder being mounted facing each other on parallel axes, the cutting edge being mounted so as to make tangential contact with the backing cylinder.
By causing the strip to pass between the blade-carrier and the backing cylinder, the strip is cut by means of continuous rotary motion. It is easy to synchronize the driving and the cutting of the strip with the travel of the sealing stations.
Preferably, the blade is curved symmetrically about a midplane of the blade-carrier, which plane extends perpendicularly to the axis of rotation of the blade-carrier.
In this way, by causing the middle axis of the strip to coincide with said plane, lids are obtained that naturally present two symmetrical tongues, thus making it easy to open a receptacle.
In a preferred embodiment, the blade is curved with a radius of curvature approximately equal to half the width of the strip, and the dimensions of the blade-carrier are adapted to make cuts that are spaced apart from one another by a distance that is substantially equal to the width of the strip.
It is thus possible to optimize strip consumption by making lids of dimensions that are just sufficient to cover the openings of the receptacles.